


Unlimited Polyamory

by RoyHankins



Category: Fate/stay night - All Media Types
Genre: Cross-Posted on FanFiction.Net, Crossovers & Fandom Fusions, Dresdenverse AU, F/F, F/M, Fluff, Knight of the Cross Saber, Nonbinary Character, Nonbinary Saber, Other, Polyamorous Character, Polyamory, White Council Apprentice Shirou Emiya, White Council Wizard Rin Tohsaka
Language: English
Status: Completed
Published: 2021-03-08
Updated: 2021-03-08
Packaged: 2021-03-14 11:55:53
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,780
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29916537
Author URL: https://archiveofourown.org/users/RoyHankins/pseuds/RoyHankins
Summary: Rin Tohsaka has it all. She's a full-fledged wizard of the White Council, she has a doting boyfriend who can cook like none other, and a strapping girlfriend who can do anything. So...why does she still want more?
Relationships: Artoria Pendragon | Saber/Tohsaka Rin, Emiya Shirou/Arturia Pendragon | Saber/Tohsaka Rin, Emiya Shirou/Tohsaka Rin
Comments: 1
Kudos: 10





	Unlimited Polyamory

Rin Tohsaka woke up in bed alone.

She knew he was gone before she opened her eyes. His warmth, his presence, which had carried her so peacefully through the night, was gone.

“Shirou,” she ordered, “come back to bed!” It wasn’t that she was grumpy. Rin was never grumpy. Merely justifiably irate. Especially before she’d had her morning coffee.

He laughed, and it was the one where Shirou thought he knew something she didn’t. She wished it wasn’t so stupidly endearing. “Rin, take a deep breath, then tell me if you want me to go back to bed.”

Already realizing what he meant, Rin did as he asked anyway, and sure enough the smell of cooking breakfast quieted her fury. “Western breakfast?” she asked, rising up with a stretch. She could already feel a pain developing in her lower back from the mattress they shared...this was what happened when she let Shirou buy their furniture.

“It’s nothing much, just a scramble.” It was like he was  _ trying _ to piss Rin off. Being faux humble was at the top of her list of things that Shirou needed to stop doing. If Rin hadn’t still been so out of it, she’d have thrown a pillow at his head. “Here, I made you this,” Shirou said, walking out of their apartment’s kitchenette and handing her a hot cup of coffee.

Maybe she needed to reorder the list. The thoughtfulness might be the worst. Grumbling internally about how he didn’t seem to think she could take care of herself, Rin took a sip and had to admit, “It’s perfect. Thank you.” It looked black, but there was a spoonful of honey in it to brighten her morning, just the way she liked it.

Shirou smiled at her, and Rin just took a moment to let that sight consume her thoughts. His red hair looked good when it was messy, which was great considering he’d never been able to tame it, even with Rin’s help. His smile: so open, so honest, completely devoid of the political shenanigans Rin was surrounded by on a daily basis. He wasn’t trying to charm her for his own benefit, because he wanted something from the heir to the Tohsaka family. He just liked her.

It wasn’t as though his expression could truly tell her all of that, but Rin knew it anyway. She let herself look into his light brown eyes, and felt like she could get lost in them. As a wizard, there weren’t many people who Rin could look directly in the eyes, but Shirou was one of them. She’d yet to truly understand what she’d seen in the Soulgaze, as each of them had been given a vision of the other’s soul, but it had made sure she knew the  _ real _ Shirou.

The fact he was only wearing his underwear, showing off his frankly gorgeous physique in the process, gave Rin more to look at too.

The moment ended, and Shirou went back to the kitchen. “I’ve got training with Saber in a few hours, lunch with Dad, training with Dad, work, then I should be getting home around 10 or 11.” He started spreading the scramble he’d made onto two plates, then brought Rin hers with a fork, while looking at her expectantly.

Hearing how packed his day was going to be put a small damper on her mood. They barely got to spend enough time together as it was, but this was going to be a particularly Shirou-less day.

Still, she had to observe her part of their little morning ritual. “I’m catching up with Sakura, sending some of my notes to the Council, meeting Saber for a date, then coming home and waiting for you.” They both knew she’d be waiting a while.

He sat next to her on the bed, and for a while they ate together in comfortable silence. It tasted amazing, because  _ of course _ it did. Rin was still a little frustrated that, while she wasn’t exactly a bad cook, she was nowhere near as good as her boyfriend or her sister.

“I’ve got some time before training?” Shirou brought up. With any other guy, Rin knew that would have been some attempt at a sly innuendo, but as things stood she needed to be the one to take the initiative on that front.

No, he actually wanted to spend time together. Because he’d seen how she felt. Rin sighed. “If I didn’t know better, I’d say you lay it on too thick.” That comment just got another beautiful smile from him, which Rin couldn’t look at without melting into a complete and utter idiot. She elected to rest her head on his shoulder instead.

“So...Saber date?” As he always, discussing Rin’s relationship with Saber made Shirou sound a little uncomfortable, like he was scared he'd step on a conversational landmine.

Once Rin had realized there was little hope of quickly curing him of that attitude, she’d decided to see it as cute. “If you’re asking what we’re doing, you’re out of luck. Saber is still intent on ‘courting’ me, and today that means they’re meeting me in the park, and after that...” She shrugged her shoulders. That was part of the fun of dating Saber, in Rin’s opinion. The knight was surprisingly romantic, and planned far more interesting outings than Shirou did.

Not that Rin favored her girlfriend over her boyfriend. For one thing, Saber was hardly any better at cooking than she was, so that was a large point in Shirou’s favor. They were also far more guarded, while Shirou was perhaps the most open person Rin had ever met. Sexually...neither had an edge, they each fulfilled a different need for Rin pretty much perfectly. Which was part of the point of being poly.

“You’re comparing us in your head again, aren’t you?” As far as she could tell, there was no reproach to his question, but she felt bad regardless.

Putting on a confident air, she told him, “Yes, but it’s still a tie. You’ll need to step up your game if you don’t want to risk becoming my second best partner.” It was all said in good humor, and it looked as though he took it as such. That was a relief. Early in their friendship, and in their relationship, he’d taken her words at face value too often. Still, she was curious about something. “Shirou, what do  _ you _ think about Saber?” He opened his mouth to reply, but she cut him off. “ _ Not _ about them as your instructor, but as a person.” Rin had a hunch.

He looked up at their apartment’s ceiling, as he thought about how to answer that. “She, uh,  **they** are nice?” Rin motioned for him to continue. “They’re always ready to help when you need them, and I’ve never met anyone as strong as Saber. I don’t just mean with their Sword. There’s something...I don’t know. Unrelenting? Indomitable? Sometimes, they look at me, and it’s like...Saber thinks they  **are** a weapon. A weapon for good...but sometimes I’m worried they don’t think about themselves enough.”

It was an interesting analysis, and not one Rin disagreed with in the slightest. Well, perhaps ‘indomitable’ wouldn’t be the best word for them. Rin had certainly made Saber beg for mercy more than once.

But that wasn’t really why she’d asked. The entire point of the question was to see past the answer he was willing to give, to the one he wasn’t. Rin smiled predatorily. “Shirou, do you have a  _ crush _ on my girlfriend?”

There was no end to the satisfaction she got from the blush that had spread across his cheeks at that. “W-what? Me, have a crush on Saber? That’s ridiculous, I...” He was babbling, making Rin fairly sure she’d hit the nail on the head.

It was looking like she’d need to dispel any notion he had that this was a problem. Leaning up, she kissed his cheek, which at the very least got him to pay attention to her again. “I don’t have an issue with you liking them, Shirou. It’s adorable, actually.” An idea came to her, and she added, “I know! Ask Saber out on a date after you’re done with training!”

It was hard for Rin to repress her laugh at how shocked Shirou looked at the suggestion. “I couldn’t...do you think they’d want to?” Rin shrugged. She didn’t know Saber’s inner thoughts, but it would do no harm to test the waters. “And you’d...be okay with that?”

Sometimes, Rin thought, her boyfriend could be an idiot. She pinched the bridge of her nose and sighed. “Shirou, we’re polyamorous. I love you, and I’m starting to fall in love with Saber. I think the two of you could be happy with each other as well.” She didn’t mention one of the more pragmatic angles underneath her reasoning: if something were to happen to her, she’d feel far better if Saber was there for him.

“You’d really be okay if I dated someone else?” He sounded unsure of the idea. Rin didn’t understand that. Sure, they’d adopted polyamory on her suggestion, and thus far she’d been the only one to date outside their partnership, but with her nod she hoped he’d understand she really had no issues with it. “What if I wanted to ask out Sakura?”

Rin blinked. Where...where had that come from? “That’s not the same at all!” Rin objected. “I said I’d be okay with you seeing  _ Saber _ , so I don’t know where you got the idea to bring my little sister into this!"

He smiled as though he’d won some victory for finding a weak spot in her argument. “So, I  _ wouldn’t _ be allowed to date her then?”

“I didn’t say that,” Rin clarified, trying not to feel foolish for her outburst. “We could strike a bargain. You can have permission to date my sister if I have permission to date yours.”

Oh how flustered he looked at that. The poor little straight boy. Well, not too straight, if he had a crush on Saber, but still. “Ilya?!” Shirou finally managed to ask. “You want to date  **Ilya** ?!” He sounded completely befuddled by the idea.

“I didn’t say that either,” Rin explained. Shirou could be ridiculously dense sometimes. “I still haven’t met her, if you’ll recall,” she said, with a pointed glare. “We’d just be giving each other permission to try.” She didn’t have to say what else she was thinking, now that the topic had been brought up.

They put their cuddling on pause so they could both get ready for the day, something that still usually felt cozy and warm since they were sharing a small studio apartment. Rin was doing her best not to feel like Shirou was ashamed of her.

Sure, he hadn’t introduced her to his sister. Or quite a few of his mortal friends. Or his father. Not that...she was particularly excited at the idea of meeting Kiritsugu Emiya. Other wizards had shared far too many horror stories about what the man had done, in his years as an assassin. And as far as she knew, Shirou had no clue that the adopted father he loved so much had once been a hair’s breadth away from being officially labeled a warlock. Even in his retirement, the Doom of Damocles hung over his head.

It also wasn’t really fair to hold it against Shirou, considering Rin still hadn’t introduced him to her father. At least Kiritsugu knew who his son was dating, Tokiomi Tohsaka wasn’t aware that his darling daughter was dating anyone, much less the apprentice of the feared Mage Killer and  **Saber** .

Pushing those thoughts to the side, Rin and Shirou left the apartment together, sharing one last kiss before splitting their paths.

For all the things that worried her about the two of them, Rin was never really  _ worried _ . There was something about her and Shirou, something she’d felt ever since they’d first met in high school. This intuition that, no matter how much either would step on the others’ toes, they’d be okay.

* * *

One meal with her little sister and a lot of boring paperwork later, Rin was sitting on a park bench, waiting for her date.

The roar of a motorcycle engine in the nearby parking lot told her the wait was finally over. Rising up, and making sure her skirt wasn’t dirty, Rin looked over and caught Saber’s eyes just as they were pulling off their helmet.

Damn Rin’s weak heart.

How was it that no matter how much time passed, it only took one look at Saber to steal her breath away? To send her blood pressure skyrocketing?

And just to make it worse, as Saber approached, they smiled, just for a moment.

When Shirou smiled, it was like the sun rising. Warm and radiant and full of life. Beautiful, but also expected.

When Saber smiled, it was a sign of trust. A small lowering of the guard from perhaps the most guarded person Rin had ever met.

The sight of it sent butterflies rampaging in Rin’s stomach.

Their outfit didn’t help matters. Saber looked  _ incredible _ in a black suit, and the way they effortlessly carried their enormous double bass case with one hand gave them a palpable aura of strength.

Saber inclined their head towards Rin. “My lady.”

“My knight,” Rin replied, wishing she didn’t love the role play they had going on as much as she did. “What did you have in mind?”

“It’s not far.” They set off, and Rin locked step beside them. It was a beautiful day, and there was something serene about this remote park. “How are Council affairs?”

It took a moment for Rin to think of something she could say to that. “Boring, as usual.” Saber nodded, and didn’t press for more.

Rin was a full-fledged wizard of the White Council, the youngest one to reach that title in centuries. Shirou was an apprentice, though he too would likely one day reach wizard status.

Saber was from a different world altogether. While their case did contain the enormous string instrument it was made to hold, there was something far more precious inside as well: a Sword of the Cross. One of three such Swords, the Knights who wielded them were almost a supernatural nation unto themselves, one always ready to stand against supernatural evils.

There were few Knights who had a career as fruitful or as well known as Saber’s. They pursued their prey as an unyielding force, though one that bowed to the niceties and politeness expected of a knight, or a member of the supernatural community. It had given Saber a powerful reputation, one that struck fear into all those wise enough to realize the price of their enmity. Thanks to their efforts, Japan was becoming safer for ordinary mortals. They wielded their blade, Amoracchius, with a passion and a skill that some thought was truly peerless.

What none of them knew, what only Rin and Shirou had been allowed to learn, was who Saber truly was, part of why the Sword was so strong in their hands.

Their True Name was Arturia Pendragon, descendant of King Arthur himself. It was a secret Rin and her boyfriend would take to the grave, if necessary.

“What has you so lost in thought?” Saber asked her, as they moved through the park.

Rin was truthful. “I find the White Council’s lack of trust in you idiotic.” It didn’t matter how good someone’s record was, or how wonderful the things they did were. If they weren’t a wizard, they were kept at arm’s length, at best.

“Considering your Council was founded by the original Merlin,” Saber replied coolly, “and the leader continues to use his name as a title, I am unsure how much I trust them.” They didn’t say more than that, but Rin knew what they meant anyway.

Whatever had happened between Arthur and Merlin, it hadn’t been good, from what Rin could tell. It was all stories from a world away, from a culture she had no real connection to, but for Saber it was a very real part of their life. How long had they had to deal with the Council? What was it like, treating with them as an outside party?

Food for thought, but this wasn’t the time for that meal. “How was training with Shirou?” Rin asked, excited to hear if her boyfriend had gone through with her suggestion.

Judging by the conflicted expression on Saber’s normally impassive face,  _ something _ had happened, at the very least. “His mind was not on training.” From Saber, that would normally be a condemnation, but there was something more curious to her tone. “He kept...staring at me, and I do not know why. When I attempted to inquire as to the change in his behavior, he found an excuse to leave my presence.”

Rin felt embarrassed on Shirou’s behalf. Perhaps her plan could have been executed in a better way. “That’s strange,” Rin told Saber, trying to find some route to possibly make this throuple idea work. The fact it could lead to the two of them getting a place with Saber, and finally getting a better apartment, had nothing to do with her eagerness. “Saber, what do you think of him?” Saber started to open their mouth, but Rin cut them off. “Not as a pupil, but as a person.”

They were getting farther from the city in their walk, moving from what was a simple park into the wooded outskirts, where the terrain was rougher and the signs of humanity less prevalent. “He has a good heart,” was what Saber decided to start with. “He’s always eager to help, he is capable of learning new skills quite quickly, and his cooking is perhaps the best I’ve ever tasted.” Then, Saber smiled, and for the first time in a while Rin got to see that expression when it wasn’t directed at her. “He is a good man trying to forge himself into a weapon, regardless of how unsuited he may be towards that goal.”

There it was. Rin could see it.

Now, she just had to strike from the right angle. “You know, he said something just like that this morning...about you.” Saber stopped in their tracks, looking a little stunned. Giving them a teasing smile, Rin suggested, “I think he might like you back, Saber.”

They didn’t take it as awkwardly as Shirou had. “That would explain his behavior.” They walked in silence for a minute or so after that, until finally Saber asked, “I assume, judging by how you are trying to entice Shirou and I towards each other, that you would not mind if I were to court him as well?”

Sometimes, Rin thought, her girlfriend could be a genius. “Yes, but only if you tell Shirou that’s what you’re doing.” She could only imagine how he’d react to this fantastically strong nonbinary woman making it clear that they would be courting him. Would they court each other? The more Rin thought of it, the more happy she was.

Underneath even her secret reasons for wanting them to get together, the deepest truth of the matter was that she thought they’d be cute together.

“We’re here.” The simple proclamation snapped Rin out of her daydream of going on a date with both her partners at once, of what things could be like as a three-person relationship.

They’d reached a clearing, now clearly outside the city limits. There was a pond, or perhaps a small lake, surrounded by trees, and there was an old wooden bench facing the water as a convenient place to sit.

It was beautiful, but there was something more to it...something ethereal. Why did this body of water feel so striking? Rin wished she could put a finger on exactly why it felt as though she was experiencing deja vu.

Had she seen something like this place during a Soulgaze? That didn’t seem right. Like anything she saw with her Sight, the effects of a Soulgaze could be recalled with perfect clarity, as though she was seeing if for the first time, and she’d seen nothing like this vista. What was it then?

“I thought you would like it. Let’s sit down, and enjoy the day.” They did as Saber suggested, and Rin laid down with her head on Saber’s lap, enjoying the privacy the area offered them.

With her mind adrift, Rin latched onto a strange question. “Do you ever wonder...what would have happened? If we hadn’t met?”

It wasn’t a night Rin usually liked to think about, regardless of what had come from it later.

A monster prowling her high school, two students with magical talent independently taking up the task of stopping it, the discovery of their shared gifts, the realization they were far in over their head, and the beautiful knight stepping in to save their lives.

“I don’t.” Saber gave their answer without much thought, as though it was something simple. “I suppose...you both would have died that night.”

An understatement if ever she heard one. If Rin ever found what inept mageling had summoned a hellhound in a mortal high school, there would be real hell to pay. “But if there had been no beast. If we’d never met...” Rin’s voice trailed off, unable to put together the rest of the thought aloud.

Saber ran a gentle hand through Rin’s hair, as though calming a child. “Pondering over what could have been has driven better wizards than you mad. Focus on what is. I am here, and  _ nothing _ can take me from you.”

Taking a deep breath, Rin tried to internalize those words, even if they went so deeply against her way of thinking.

There was so much on her mind, all the time, it sometimes felt difficult to keep up with it all.

The Black Court had been spotted in the area, and some were beginning to suspect the Matou’s were involved in some alliance with the monsters.

There was enormous pressure on her to continue her research into what other worlds lay within the boundaries of the Outer Gates.

There were two people in her life that she held dear, and juggling them without favoring either could be stressful.

But none of that mattered in the moment. She could rest for as long as she needed, knowing Saber was there for her, and that at the end of the day, Shirou would share her bed.

It wasn’t much. But it was enough.

**Author's Note:**

> This felt super self-indulgent to write, so please let me know if you want more of this polycule/more Dresdenverse AU with these characters. I ended up thinking of a LOT of fun ways to translate Fate/stay night stuff into this verse.


End file.
